1. Technical Field
The disclosure generally relates to a method for soldering an LED (light emitting diode) to a circuit board, and particularly to a method for soldering an LED to a circuit board by surface mounting technology (SMT).
2. Description of Related Art
In recent years, due to excellent light quality and high luminous efficiency, LEDs have increasingly been used as substitutes for incandescent bulbs, compact fluorescent lamps and fluorescent tubes as light sources of illumination devices.
Generally, surface mounting LEDs are more and more popular. To solder the surfacing mounting LEDs to a circuit board, solder pastes are used, which are deposited on predetermined regions of the circuit board in advance; then the LEDs are positioned on the solder pastes. Thereafter the solder pastes are heated to melt by a reflow process to electrically and mechanically connect the LEDs with the circuit board after the melted pastes are cooled to become solder balls. However, since each solder paste is a single solder block if during the reflow process heat is unevenly applied to the solder pastes, the melting degrees of the solder pastes will be different from each other. When this happens, due to different cohesions, the solder balls obtained from the melted solder pastes after they are cooled will have different shapes and heights. The different cohesions during the melted solder pastes cooled into solder balls may also be caused by different qualities of printing in applying the solder pastes onto the circuit board. The different heights of the solder balls will cause an unsatisfied electrical and mechanical connection between the LEDs and the circuit board, which may unfavorably affect a light output of the LEDs and useful life of the LEDs.
What is needed, therefore, is a method for soldering a surface mounting LED to a circuit board to overcome the above described disadvantages.